A known jet printing head comprises a chamber suited to hold an inking liquid, one of its wall having nozzles uniformly disposed in rows and representing capillary holes. Each nozzle has a pair of electrodes separated by an insulating rod whose conical end faces the nozzle.
The nozzle also has a conical inlet and a cylindrical outlet connected therewith. As pulse voltage is applied to the electrodes, the liquid in the respective nozzles is instantaneously heated whereby a maximum pressure characteristic of pin-point microexplosions is produced at the cylindrical outlet of the nozzle. The inking liquid is discharged from the nozzle onto a data medium to make a corresponding record.
One of the disadvantages of such a structure is associated with unwanted complexities involved in production of a nozzle having conical and cylindrical sections which should be made to a high accuracy because even a slight deviation from preset parameters impairs geometry of a drop of inking liquid coming out of the nozzle, a factor adversely affecting printing quality. Likewise the insulating rods should meet stringent requirements for accuracy in production and installation. This calls for the use of precision equipment and skilled labour, which substantially increases the cost of such a printing facility. Furthermore, frequent drastic temperature changes in the liquid cause wear of the electrodes and the rod. Also, the liquid should be often changed due to its disintegration in heating.
There is further known a printing head with an electric means for supplying a conducting liquid dye staff to a data medium, which comprises an inking chamber with an assembly suited to supply said liquid dye staff and having a plurality of tubes of a sufficiently large diameter, said tubes being essentially capillary nozzles. The known printing head comprises a multitude of pairs of electrodes, each of which is fitted on diametrically opposite sides of the tubes at right angles to the tube axis, as well as a permanent C-magnet encompassing the head so that the magnetic field of the magnet passes through all the holes. On application of a voltage pulse to a pair of electrodes, they will pass current due to electric conduction of the liquid. As said current interacts with the field of the permanent magnet, there is produced an electrodynamic force ejecting a drop of inking liquid from the given capillary tube. Although a fairly small current passed through the electrodes does not cause their failure and disintegration of the inking liquid, the construction of the disclosed printing head is rather complicated due to the need for inserting the electrodes in the capillary tubes and aligning them in a precise manner relative to the tube axis. If the alignment is not exact, printing quality of drastically impaired. Moreover, it is practically impossible to connect the electrodes securely to current buses. Finally, a reliable discharge of drops of inking liquid from the head nozzles necessitates similar conditions for each capillary tube, that is, a similar magnetic field in the zone where the electrodes are positioned and similar strength of a current pulse flowing therethrough. In the case of a C-magnet the magnetic field in the centre is much weaker than that round the periphery, a factor substantially affecting printing quality due to impaired formation of drops of liquid discharged from the capillary tubes. Furthermore, the size of the C-magnet must exceed by many times the area occupied by the capillary tubes to obtain an essentially uniform field over the entire area of the printing head.